Ares I Upper Stage change – receives additional capacity

February 6, 2007 by Chris Bergin

NASA Constellation have decided to increase the propellant capacity of the Ares I Upper Stage tanks, despite moving to a common bulkhead design – which initially shortened the vehicle by 60 inches in length.

The latest Upper Stage change returns the vehicle to a previous Design Cycle configuration, while keeping the recent mass saving move to a common bulkhead. These changes are believed to be responsible for the delay to the completion of the Upper Stage SRR (Systems Requirement Review).Huge amounts of VSE related insider news and presentations are available for download on L2. See list at the end of this article.

The stretching of the propellant tankage – by about five feet – will increase of the amount of additional capacity in the tanks by an estimated 11,650 pounds, whilst returning to the length of previous Upper Stage design for the DAC-1C vehicle design.

The elimination of the intertank from the Upper Stage was initially used to save mass. The decision to instead translate the saving into larger propellant tanks will have a number of potential benefits. However, it is expected to have a slightly negative effect on the Upper Stage’s initial acceleration, reducing it to around 0.6 G.

The Upper Stage SRR conclusion on this current Design Cycle, which was delayed from the start of the year, is now expected to be completed by March at the earliest. The SRR was initially believed to be delayed due to a potential move to a 6.3 diameter Upper Stage option. That was recently dismissed as an option by Constellation.

‘The Exploration Launch Office Chief Engineer, along with polling members of the TIM, recommended going with common bulkhead configuration due to the dry mass savings of 2,165 lbm needed to close the payload requirement,’ noted Constellation’s Steve Cook.

‘On day two of the TIM, the US Chief Engineer presented a Risk assessment for the following three different configurations: Separate Tanks, Common Bulkhead with a 5.5-meter diameter, and a Common Bulkhead with a 6.3-meter diameter.

‘The high risks in performance estimate savings, schedule, and cost supported the TIM recommendation of not going forward with a 6.3-meter diameter design configuration.’

At around the same time as Constellation decided on lengthening the Upper Stage, ATK updated their figures that show the predicted weight of the 5-segment Solid Rocket Booster – which will be the first stage powerhouse for the Ares 1 Crew Launch vehicle – has dropped by around 10,000 pounds over recent months.